According to the National Cancer Institute, breast cancer is second only to lung cancer in causing the deaths of American women. An estimated one in eight women (12.6%) will develop breast cancer in their lifetime. More than 180,000 women per year are now diagnosed, often too late for lifesaving treatment. Early diagnosis is critical to early and successful treatments for most breast cancers. MRI has great potential as a tool for imaging and spectroscopy based diagnosis of breast cancer in women, especially for those under 50 years of age. Younger women frequently have "radiodense" breast tissue, rendering breast cancer diagnosis with conventional mammography problematic. For this reason and others, contrast-enhanced MRI of the breast has emerged as one of the most promising clinical tools for detection of breast cancer and delineation of its anatomic extent. MR spectroscopy of tumor metabolism may further augment imaging diagnostic methods. To encourage the promise of magnetic resonance based diagnostics, the NCI has issued at least a dozen program announcements over the past decade specifically requesting grant applications for MR based investigation of breast cancer. The NCRR has also broadly supported the development of NMR methods and technology for cancer research. [unreadable] [unreadable] Based on our preliminary results, we believe that significant improvements in MR based diagnoses of breast cancer can be had at 4T, compared to 1.5T where a predominance of breast MRI is now performed. To test this hypothesis however, we must first develop the new RF technology to do so. To reproduce the favored clinical approach for breast imaging at 1 ST, we must develop high SNR dual breast receiver coils together with a high homogeneity body transmitter coil currently not available for 4T human imaging. Our hypothesis (improved breast cancer diagnosis with new coils at high fields) will be tested on two hundred women being screened for breast cancer. The hypothesis will be proved by improved diagnostics results at 4T compared to 1.5T. We attribute this expected rate improvement in breast cancer diagnosis to increased specificity and sensitivity gained from the increased signal-to-noise, spatial resolution, contrast, spectral resolution, and fat suppression inherent to 4T. The IW technology development proposed will be required to realize the full 4T benefit.